1. Field of the Invention
The present invention is related to a reluctance-type motor which is used as a drive source replacing the conventional D.C. motor and induction motor with an inverter, and particularly can be used when a long and narrow motors, having a small diameter is needed rather than a flat-type one.
2. Description of the Related Art
Since reluctance-type motors have more magnetic poles than D.C. motors, they are difficult to make and have not ever been put to practical use.
Reluctance-type motors are well-known in the art. Reluctance-type motors provide a very low rotational speed and a large output. They have only partly been used for the arm of a robot as a direct drive unit of a load, but are not commercially available.
Reluctance-type motors are somewhat used as a small stepping motors, and wide application therefore has not been developed as yet.
It is difficult to construct a reluctance-type motor having a small diameter and a large output torque since the number of the magnetic poles is large as compared with a D.C. motor.
To explain, by taking a three-phase, full-wave motor of the reluctance type as an example, the number of magnetic poles and salient poles is large, the construction is complicated, and there are six systems of exciting coils. There are at least 12 poles and exciting coils are for a three-phase full-wave energization.
Also, the number of the salient poles of the rotor is at least 14, which is very large. Accordingly, there is a problem that it is difficult to construct a motor having a small diameter.
Further, since the number of times the magnetic energies of the magnetic energies of the magnetic and poles enter and exit during one rotation increases, there is an inconvenience that an increase of the rotational speed is difficult and iron loss increases.
Next, the second problem is that the magnetic energy stored in the exciting coils is remarkably large and a certain time is required for storage. Therefore, the rise of the energization current delayed and a reduced torque occurs.
In addition, some time is required for the magnetic energy to disappear, which causes a counter-torque. The occurrences of the reduced torque and counter-torque increase as the rotational speed rises. Consequently, there is a problem that the efficiency degrades and the rotational speed becomes extremely small. The present invention overcomes the above-mentioned problems.